The present invention relates to a floor vibration-damping apparatus for damping a horizontal vibration of a floor, based on an earthquake, on which vibration sensitive office automation equipment, such as computers, is provided.
For example, Japanese Published Unexamined Patent Application No. 62-86265 (corresponding to U.S. Pat. No. 4,805,359 issued on Feb. 21, 1989, discloses a floor vibration-damping apparatus whose main portion is illustrated in FIG. 18. A movable supporting portion B having steel balls b supports a flat floor construction F which is made of H-shaped steel and can move horizontally with a low resistance. Damper working portions A are provided between the floor structure F and a fixed floor C.
FIG. 19 shows a construction of the damper working portion A in detail. A shallow and flat circular vessel a1 is fixed to the fixed floor C, and accommodates a viscous fluid a2. A horizontal resistance plate a3 is submerged in the viscous fluid a2 in parallel with the bottom surface of the vessel a1, and a distance therebetween is a constant d. This resistance plate a3 is fixed to the floor structure F by a rod a4.
Tension coil springs E are provided in four directions at right angles with respect to one another in a neutral position of the resistance plate a3. The outer end of each coil spring E is fixed to the fixed floor C by a fixing device e, and the inner end thereof is coupled with the rod a4 as a resistance input portion of the floor structure F through a hard rod G and a flexible chain g. The hard rod G reaches a surrounding wall of the circular vessel a1 which acts as a reaction base, and an end portion of the rod G is fixed to a stopper H which touches the inner surface of the side wall of the vessel a1. A chain g is connected between a position at the stopper H and the rod a4.
Pretension of a predetermined value is previously applied to the coil spring E of each direction for a trigger function. The trigger value is set so that the stopper H applies the reaction to the surrounding wall of the vessel a1 and no load is applied to the rod a4 at the neutral position. In a case that the floor structure F receives the horizontal input based on the earthquake or the like, if the horizontal input is lower than the trigger setting value of the coil springs E, the horizontal movement of the floor structure F is restricted perfectly and the floor structure F does not move.
However, if the floor structure F moves horizontally by receiving the horizontal input larger than the trigger setting value, the resistance input plate a3 moves simultaneously and the coil spring E in the pulling direction position is extended. At this time, the viscous resistance received by the resistance input plate a3 acts as an attenuation force and prevents an excessive displacement of the floor structure F. The tension force of the coil springs E applies the recovery force to return the floor structure to the original position.
In the floor vibration-damping apparatus disclosed in the above Japanese Published Unexamined Patent Application No. 62-86265, a cover is slidably put on the upper opening of the vessel a1 which accommodates the viscous fluid a2. However, the opening is not perfectly sealed by the cover so as to allow the resistance plate a3 and the rod a4 supporting it to move. Thus, it is troublesome to carry the damper working portion A from a factory to a building site to set and manage it. In addition, alien substances, such as dust may mix with the viscous fluid a2 during and after the installation of the vibration-damping floor. If so, characteristics of the viscous fluid a2 may change, and especially the coefficient of viscosity may change, so that the damper characteristic may change. The viscous fluid a2 may be added to the damper working portion A. In this instance, maintenance may be necessary.
It is well known that the viscous resistance applied to the resistance plate a3 in the viscous fluid a2 is inversely proportional to the distance d between the plate a3 and the bottom surface of the vessel a1. In order to set and maintain precisely the distance d, the horizontal accuracy of the resistance plate a3 and the vessel's bottom surface are important. For this end, high accuracy is required during installation. In addition, the distance d may be expected to change in accordance with the installation error of the vibration-damping floor, the load against the floor for the usage period and the secular change. However, it may be impossible to adjust the distance d during the usage period, and it may be very difficult to maintain the damper characteristics. In order to set the resistance plate a3, the damper working portion A needs many components to mount a mounting plate a5 at the floor structure F, thereby increasing the cost of the floor vibration-damping apparatus.
In the floor vibration-damping apparatus disclosed in the above Japanese Published Unexamined Patent Application No. 62-86265, the floor structure F consists of the movable supporting portion B and the damper working portion A independently. This construction is shown in FIG. 20 which is a plan view of the floor structure F, wherein the movable supporting portions B are positioned at apices of squares having about 2 m sides and each of the damper working portions A is positioned at the center of each square. In other words, they are positioned in due consideration of the supporting of the floor structure F and the force balance of the earthquake. Thus, there is a complex construction under the floor of the floor structure F, and it is difficult to design and install the floor vibration-damping apparatus with maintaining accurate spacing.